Mastixiopsis nyssoides KIRCHH., 1936, 1993

Manchester, Steven R. & Collinson, Margaret E., 2022, Mastixioid Fruits (Cornales) From The Early Eocene London Clay Flora: Morphology, Anatomy And Nomenclatural Revision, Fossil Imprint 78 (1), pp. 310-328 : 318

Mastixiopsis nyssoides KIRCHH., 1936

Text-fig. 5a–g

R e m a r k s. Mastixiopsis is an extinct genus which was first recognized from the Eocene of Riestedt , Germany ( Kirchheimer 1936). The fruits are unilocular with a locule that is curved in cross section ( Text-fig. 5l, m ). The germination valve extends over the entire length of the endocarp (Kircheimer 1936). We reexamined the type material and used Scanning electron microscopy to document the pericarp anatomy ( Text-fig. 5n ). The endocarp is a dense tissue composed of fibers and sclereids and is surrounded by a thick mesocarp of larger anticlinally oriented cells (Textfig. 5l–n) .

In his concept of Mastixiopsis nyssoides KIRCHH., Mai (1993) included a specimen called “? Mastixia cantiensis M. CHANDLER, 1962 (non Reid and Chandler 1933)” by Chandler (1962: 122–123, pl. 18, figs 1–3) from the early Eocene Dorset Pipe clays at Arne, UK. That specimen is refigured here ( Text-fig. 5a, b ). However, Mai was unable to study the original material and stated “without the knowledge of the originals, it is not possible to decide whether this determination is also correct for the typical Mastixia cantiensis E.REID et M.CHANDLER (1933) from the London Clay.” ( Mai 1993: 59). We encountered two additional specimens of the same kind from the London Clay of Sheppey. One of them ( Text-fig. 5c, e, g ) was listed as a specimen of M. cantiensis by Reid and Chandler (1933), and the other ( Text-fig. 5d, f, h ) was cited by the same authors as the paratype of Mastixia grandis REID et CHANDLER (the holotype of which we now treat as Tectocarya grandis ). We re-examined the type material of Mastixopsis from Riestedt for comparison ( Text-fig. 5i–n ).

The type material of Mastixiopsis nyssoides from the Eocene of Riestedt shows prominent external longitudinal grooves ( Text-fig. 5i–k ). These grooves are also seen in the Arne specimen ( Text-fig. 5a using pl. 18, fig. 1 in Chandler 1962), but they are not obvious on the outside of the pyritized Sheppey specimens ( Text-fig. 5c, d ). The undulatory contact between the epicarp and mesocarp as seen in transverse sections ( Text-fig. 5f, h ) may be an indication of those grooves but the spacing lacks the uniformity of the grooves in Text-fig. 5a and Text-fig. 5i–k . The anatomical composition of the London Clay specimens conforms well with those from Riestedt, including the mesocarp of anticlinally oriented elongate cells and the more dense inner sclerenchymatous layers forming the endocarp. Future CT study of the Reistedt and Arne specimens and the London Clay specimen in Text-fig. 5e, f, h will be helpful to confirm if all of these belong to the same taxon .

Figures

Text-fig. 5. Mastixiopsis nyssoides KIRCHH. a, b, g–n: Organic preservation. a, b: Lignitic, unpermineralized, early Eocene Dorset Pipe clays at Arne, V. 40762. a: Ventral view (original illustration from pl. 18, fig. 1 of Chandler 1962). b: Transverse fracture, somewhat distorted by compression. c–f: Pyrite permineralization. c: Ventral view, V. 22963(1) from Sheppey, originally listed as Mastixia cantiensis. d: Lateral view, V. 22969 from Sheppey (identified as Mastixia grandis by Reid and Chandler 1933: pl. 25, fig. 8). e: Equatorial transverse physical section from (c). f: Equatorial transverse physical section from (d). g: Detail of pericarp from (e), showing endocarp formed of dense fibrous tissue, surrounded by mesocarp of anticlinally oriented larger cells. h: Detail of pericarp from (f). i–n: Type material from Eocene of Riestadt, Germany, MNB. i: Ventral view. j, k: Ventral and apical views of holotype. l: View of the transversely fractured surface from (j) showing horseshoe shaped locule. m: Equatorial transverse physical cut of the specimen in (i); note yellow resin cavity (arrow). n: Scanning electron microscopy of pericarp from (l) with locule lining at lower edge of image. Note dense endocarp tissue composed of small cells (fibres and sclereids), extending about 3/5 of distance to periphery, surrounded by mesocarp of larger, anticlinally oriented cells. Scale bars 1cm in (a–f), (i–k), 1mm in (g), 2mm in (h), 3mm in (l), m, 250 Μm in (n). Bar in (d) applies also to (c). Bar in (l) also applies to (m). Bar in (i) also applies to (j) and (k).